Within drug delivery it may be of vital importance to maintain purity of a product to be administered from its production to its administration. Many drug substances are therefore supplied in sealed containers having penetrable access means, such as rubber septa, which are adapted to be pierced by a suitable tool, e.g. a hollow needle.
For example, people with IDDM frequently attach an injection needle to their insulin pen to thereby penetrate a self-sealing rubber septum of an insulin containing cartridge and establish a delivery line for subcutaneous administration. The needle and the insulin are stored in respective sterile environments until the point of connection.
Some pharmaceutical drugs adapted for parenteral administration are only stable in the administrable form a relatively short period of time. For convenience reasons, and in order to extend the shelf life of such a drug, it is sometimes preferred to store individual constituents of the drug separately and to mix them only just before a dose is needed.
Traditionally, a mixing of two substances stored in separate vials is performed using a syringe with a needle to withdraw the substance from the one vial and inject it into the other vial. The syringe with the attached needle is then used to withdraw from this vial the desired amount of drug to be injected into the patient. Oftentimes, the needle used for transferring the substances must be replaced by another needle for the actual administration of the drug.
This kind of manual operation may be cumbersome and may bring about some uncertainty as to the exact concentration of the resulting drug, because it can be difficult to completely empty a vial by such an approach. Moreover, since the first substance is withdrawn from one vial and transported to another vial via a syringe with a needle, typically including a penetration of two rubber septa in order to establish fluid connection to the respective vial interiors, both sterility and safety (in terms of e.g. risk of needle stick injuries) may be compromised. To reduce the risk of contamination of the administrable substance it is customary to clean the respective rubber septa with an alcohol swab before needle penetration. This, however, is often considered a hassle by the user, especially if she/he needs to mix the substances and administer the resulting drug quickly to avert a serious situation.
U.S. Pat. No. 5,466,220 (Bioject, Inc.) discloses different examples of drug vial mixing and transfer devices comprising one or two vials and a syringe pre-aligned and packaged in sealed sterile packages to eliminate the need for swabbing the vials before piercing and to avoid sharp needle exposures. While overcoming some of the drawbacks of the traditional way of mixing substances, the solutions comprising two vials appear bulky and operationally cumbersome, and the solutions including a single vial introduce a risk of carrying out the individual operational steps in a wrong order, because the syringe plunger is operable before connection of the vial and the syringe, thereby enabling unintended delivery of some of the syringe contents to the exterior of the vial.
WO 97/46203 (Applied Research Systems ARS Holding N.V.) discloses a pre-assembled pack for a drug reconstituting device, which pack comprises a vial co-axially aligned with a cartridge and separated therefrom by a double-ended needle element. In the pre-use state of the device the needle element is shielded at each end by a slidable bung, providing for closed, sterile needle chambers. Like the above mentioned prior art solutions including a single vial, this pack also lacks a mechanism which prevents it from being manipulated erroneously to e.g. expel the contents of the cartridge before fluid connection to the vial has been established.
EP 0 565 103 A1 (Nissho Corporation) discloses a bedside mixing arrangement comprising a drug vial, a solvent bag, a double-pointed hollow needle, and a guide capsule with a cap rotatably mounted thereon. The cap serves as a means for driving the drug vial towards the solvent bag for establishment of fluid connection between the two via the double-pointed hollow needle. To mix the drug and the solvent, firstly the cap is operated to cause the fluid connection to be established, then the entire arrangement is turned upside down allowing the solvent to flow into the drug vial to mix with the drug, and finally the entire arrangement is turned upside down again to transfer the drug solution to the solvent bag. This mixing procedure is slow and cumbersome given the size and flexibility of the solvent bag. Furthermore, the dimensions of this arrangement make it ill-suited for being carried about in connection with regular ambulatory use.
WO 2011/088471 (Bayer Healthcare LLC) discloses a device comprising a receptacle, a spike assembly having a perforating shaft and a connector element for receiving a syringe, and an actuating mechanism for automatically causing the shaft to perforate a closure of the receptacle upon rotation of an outer cover surrounding the spike assembly. While this device ensures that fluid communication between the spike assembly and the receptacle is established before a syringe is even capable of being attached to the spike assembly, it does not overcome the problems of potential premature activation of the syringe piston. Moreover, in principle the connector element needs to be swabbed before attachment of the syringe to secure a reasonable level of cleanliness during the mixing procedure. This requires additional operational steps to be performed by the user, prolonging the time needed to prepare a drug product for administration.
Especially for people who must administer a therapeutic agent several times during the day it is of importance that a portable delivery device is compact such that it takes up as little space as possible in e.g. a bag or a pocket. If the delivery device is a syringe type device comprising a piston which is slidable in a tubular reservoir in response to an operation of a piston rod, and if the device is prefilled with the therapeutic agent, or with a component therefore such as a solvent or a diluent, the axial dimension of the device must be at least twice the axial dimension of the reservoir in order to enable complete emptying thereof, because the piston rod has to extend beyond the reservoir a distance corresponding to the full stroke of the piston in the pre-use state of the device.
WO 2009/108847 (Becton, Dickinson and Company) discloses a prefilled syringe with a two piece piston rod comprising a first piece slidably mounted to a second piece, allowing the piston rod to be extended from a compressed length to an extended length by application of an axial force in the proximal direction.
While such a solution may reduce the overall dimension of the syringe in the storage condition, it adds to the number of operational steps a user must perform in order to prepare the syringe for administration of its contents. Whereas an ordinary prefilled syringe may be operated to expel its contents immediately upon removal from its packaging the preparation steps for the syringe disclosed in WO 2009/108847 include 1) removing the syringe from the packaging, 2) applying an initial axial force to one of the piston rod pieces in the proximal direction to cause disengagement of the locking elements interlocking the two piston rod pieces, and 3) applying a continuous axial force to the piston rod in the proximal direction so a locking element of the first piston rod piece engages with a locking element of the second piston rod piece.
It is therefore desirable to provide a solution of the type disclosed in WO 2009/108847 which does not entail any additional operational steps for a user.